When a molecule of a liquid approaches the surface, it experiences
a force barrier that tries to keep it in the liquid. It thus has to do
work to escape and loses some of its kinetic energy when it leaves.
that a water molecule can evaporate from the liquid if it hits the surface
from the inside with a kinetic energy greater than the thermal energy corresponding
to the temperature of boiling water, 100 oC. Use this to estimate
the numerical value of the work 'W' required to remove a water molecule
from the liquid.
- Even though the average speed of a molecule in water below the boiling
point corresponds to a kinetic energy less than 'W', some molecules leave
anyway and the water evaporates. Explain why this happens.
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Page last modified
October 30, 2002: H&T05